A one way hash of an IPv4 address is no more private than the address itself. If you know the has algorithm, you can build a rainbow table of all the hashes in under a second. Even with a random salt it doesn't take long to build a rainbow table with all possible salts.
To an extent, but there are easy ways to cut the search space. For example, you could make a unique request with garbage on it from a known IP every day, and then all you have to do is build a rainbow table for that one IP to find out what the salt is for each day, and then you can fully reconstruct the logs.
